The present invention relates to a deaerator and a deaerating method which performs deaeration for removing gaseous components dissolved in a liquid, and more particularly to a deaerator and a deaerating method which can perform the deaeration by continuous processing without using batch processing.
Conventionally, in supplying a liquid using a narrow pipe such as a hydraulic circuit, due to the generation of bubbles in the inside of the pipe, there may arise a trouble in supplying the liquid and hence, the liquid is preliminarily deaerated thus suppressing the generation of the bubbles.
In such a case, usually, the deaeration is performed such that a liquid to be deaerated is stored in the inside of a depressurizing device, and air in the inside of the depressurizing device is exhausted by suction using a vacuum pump or the like thus reducing the pressure in the inside of the depressurizing device. Since it is necessary to hermetically seal the depressurizing device in performing the deaeration, deaeration is performed by batch processing.
Although such deaeration by batch processing has an advantage that a large quantity of liquid can be processed at a time, the batch processing is the discontinuous processing and hence, the batch processing has a drawback that oil which is not exchanged for a relatively long period such as a working fluid which may be represented by oil used in a hydraulic brake of an automobile or oil used in a hydraulic circuit of a construction machine, for example, cannot be periodically deaerated besides predetermined timing for exchange.
Further, in the inside of the depressurizing device, an atmosphere exposure surface which constitutes a contact surface between the stored liquid and atmosphere is relatively large and hence, there also exists a drawback that air is again dissolved into the liquid from the atmosphere exposure surface after the deaerating processing so that it is difficult to maintain a deaeration effect.
Accordingly, as a device which performs the deaeration of a liquid by continuous processing without batch processing, there has been proposed a device which includes a vacuum vessel in which the degree of vacuum is increased preliminarily and a pipe which supplies the liquid to the vacuum vessel, and performs the deaeration by continuously supplying a processing liquid to the inside of the vacuum vessel (for example, see patent document 1).
Further, as another device, there has been also proposed a device which performs deaeration by forming fine bubbles by generating the cavitation in a liquid to be deaerated and by removing these fine bubbles (for example, see patent document 2).
Under such circumstances, inventors of the present invention have found, in the course of studying a cavitation phenomenon in a liquid, a phenomenon that when the super cavitation which is one mode of the cavitation phenomenon is generated, a cavity is formed stably in the inside of a pipe through which a liquid is made to flow (for example, see non-patent document 1).
Further, the inventors of the present invention also have found that the inside of the cavity which is formed in the inside of the pipe due to the super cavitation is stably held in an extremely low pressure state which is close to the vapor pressure of the liquid and hence, gas which is dissolved in the liquid contacting the cavity is separated into the cavity, that is, the deaeration of liquid is performed in the cavity formed in the inside of the pipe.
Patent document 1: Japanese Patent laid-open hei07(1995)-132201
Patent document 2: Japanese Patent laid-open hei03(1991)-118803
Non-Patent document 1: Seiichi Washio and three others,
“observation of cavitation inception in hydraulic oil flow”, collective treaties of Japan Society of Mechanical Engineers, Corporate Juridical Person Japan Society of Mechanical Engineers, May 1999, Vol. 65, No. 633, B edition, p. 1643-1651.